Bests & Worsts Reviews from Amazon

I cannot speak for the flea killing ability of this product, as I just put it on my cat last night. You put the product at the base of the cat's skull, right around where their collar sits, so that they can't lick it. This morning I found that the product had somehow reacted with my cat's collar and formed some sort of glue/tar that had stuck her fur to her collar. I have uploaded a picture of what happened. She is a little white cat who had a cute little black collar, but now she has a nice patch of black tar hair that will need to be shaved off in order to ever get it off of her. Water doesn't seem to get it to come out and maybe some heavy washing will get it to fade (I hope) My recommendation would be to take off any collar and wait for the product to dry a bit before putting the collar back on, if possible.